The goal of the proposed research is to determine how information is represented, transmitted, transformed and distributed by the collective activities of a group of neurons and used by the animal to control behavior. All of these processes must be defined to establish the existence of an ensemble neural code. The neural and muscular systems controlling the crayfish claw have been selected for study because variables of interest can be monitored, controlled and related directly to the animal's behavior. Planned experiments will 1) measure the influence an ensemble of proprioceptors has on motoneuron activity, 2) define how individual receptors modulate the effectiveness of other receptors' synaptic actions, 3) determine how the relationships among the proprioceptors and motor neurons change as a function of the animal's behavioral state, and 4) help elucidate the gating or switching mechanisms which mediate such changes. To accomplish these objectives the static connectivity and dynamic interactions among the sensory receptors, interneurons and motor neurons, during both active and imposed dactyl movements, will be studied using intracellular recording techniques, cross-correlation analysis, and other statistical methods for spike train analysis. An additional objective will be to determine directly the operational significance of naturally generated sequences of motor neuron action potentials produced by the motor neurons. This will be accomplished using a spike train playback technique. Activities of the motor neurons will be recorded, then played back to stimulate selected cells. The effects of several relevant variables can be assessed since a) the various input spike trains can be added or deleted, b) the temporal relationships can be shifted and c) muscle length and the inputs (activation history) preceding given spike sequences can be varied.